The hot CO.sub.2 determines the thermal residence of the energy level, wherein in addition to the oscillatory energy of the nuclei which oscillate with respect to one another there is added to the molecule the rotational energy of the rotating molecule. A quick cooling of the working medium causes a partial "freezing" of the upper laser level. Through molecular impacts there occurs a deactivation of the lower level through which occurs the residence inversion required for the laser action.
Known arrangements of gas-dynamic optical transmitters of the above type utilize a parallel connection of a number of two-dimensional Laval nozzles, wherein the dimensions of the nozzle throat are approximately 0.8 to 1.0 mm., the nozzle length is approximately 4 cm. and the nozzle width approximately 1 cm. The hot working medium, for example CO.sub.2, flows at supersonic speed through the nozzle in a z-direction and expands therein in an x-direction. In the case of the CO.sub.2 -laser there is required an expansion ratio between the transverse dimension of the nozzle throat and that of the nozzle outlet of approximately 10 to 20. In the CO-gas-dynamic laser the required expansion ratio is around 100 so that the nozzles in such devices are correspondingly longer. The above-mentioned nozzle lengths are required by the characteristics of gas flow to assure against separation of the gas stream. However, this construction has the disadvantage that the time of transit therethrough is too long so that only a relatively slow cooling occurs and therefore the upper laser level does not freeze completely because it partially follows the cooling. This leads to a lesser residence at the upper laser level and thereby results in a smaller power development. Particularly during a pressure increase this is noticeable because the deactivation by molecular impacts occurs still more rapidly. Thus, it is not possible to utilize high gas densities in the building of gas-dynamic lasers with a high output.
The purpose of the invention is to overcome these disadvantages and to produce an arrangement which permits a complete "freezing" of the upper laser level.
This purpose is attained by arranging a plurality of three-dimensional expanding nozzles in parallel connected relationship above one another and/or side-by-side. In this manner, the nozzle length can be very substantially shortened while maintaining the same nozzle throat diameter, the same expansion ratio and approximately the same inclination of the wall surfaces with respect to the flow direction z. This provides for a more rapid expansion and thereby provides for a very rapid cooling and a consequent complete freezing of the upper laser level because in the shorter time period correspondingly less molecules are deactivated by impacts. From this results the possibility of an increase of the gas density and thus a further increase of the power output.
In various exemplary embodiments it is provided that the individual nozzles be constructed rectangularly or hexagonally similar to a honeycomb. Also an embodiment is provided in which the nozzle throat is constructed circularly and ends in a rectangular or a hexagonal funnel.
Furthermore it is provided that the nozzle wall surfaces are curved concavely so that they convert the gas flow, after an initial strong inclination or expansion at the nozzle throat, into a parallel flow at the end of the nozzle. To accomplish this, there is provided an almost parallel alignment of the nozzle walls during the joining thereof at their nozzle ends. Further it is provided that the nozzle surfaces are polished smooth to avoid flow losses due to laminar or tubulent boundary layers at the edges. Still further means are preferably provided for cooling the nozzles particularly near the throat by a cooling fluid. To improve the cooling function the parts can be made from a metal having good heat-conducting characteristics (for example copper).
If very small nozzles are to be constructed, then it is suggested that the nozzle throat and the nozzle funnel be constructed circularly.